The present invention relates to a DNA containing a cDNA sequence coding for a human luteinizing hormone-human chorionic gonadotropin receptor protein (human LH/hCG receptor protein), the human LH/hCG receptor protein, and a method for preparing the protein.
The human luteinizing hormone-human chorionic gonadotropin receptor proteins (human LH/hCG receptor proteins) exist in the Leydig cells in the testis, the theca cells in the ovary, the granulosa cells, the corpus luteum cells and the interstitial cells, and play a central role in reproductive physiology. In the male and the female who is not pregnant, the LH/hCG receptor proteins are acted on only by luteinizing hormone (LH) produced in the anterior lobe of the pituitary and secreted therefrom. In the pregnant female, however, the LH/hCG receptor proteins in the ovary are acted on also by human chorionic gonadotropin (hCG) produced by the placenta.
LH and hCG are members of a family of glycoprotein hormones also including thyroid-stimulating hormone (TSH) and follicle-stimulating hormone (FSH). Each of these four hormones has a molecular weight of 28 to 38 kD, and is a heterodimer glycoprotein in which a specific .beta. subunit relating to receptor binding specificity is bound to an .alpha. subunit common to these hormones. The glycosyl moiety of these hormones seem to play an important role in signal introduction. The .beta. subunits of both LH and hCG are closely related to each other in their structure. These two hormones bind to the same receptor and induce the same biological reaction. The similarity between these glycoprotein hormones and the action by these hormones on the receptors to enhance the activity of adenylate cyclase mediated by G-proteins reveal that these receptors have a common mechanism of hormone-induced activation. The increases of adenosine 3',5'-monophosphate (cyclic AMP) necessarily lead to the synthesis and secretion of steroids. A family of G protein-coupled receptors are identified whose members are characterized by the common structural feature of having seven transmembrane domains which are known to relate to the signal introduction and binding to small ligands. On the other hand, TSH and FSH receptors have been compared with the LH/hCG receptors. As a result, of the G protein-coupled receptors, these receptors of the pituitary glycoprotein hormones are characterized by the presence of a large glycosylated domain which is grafted onto a structure containing seven transmembrane segments and putatively considered to be positioned on the outside of cells.
The structure of the LH/hCG receptors have not been elucidated so well yet, because the receptors are present in very low amounts and sensitive to proteolysis. For rat and porcine LH/hCG receptors, however, complementary DNAs (cDNAs) of these receptors are isolated and the amino acid sequences thereof are also deduced from these DNAs [Science 245, 494 (1989) for rats and Science 245, 525 (1989) for pigs].
For the rat and porcine LH/hCG receptors, the structure thereof has been thus elucidated. For the human LH/hCG receptors, however, the structure thereof is not revealed. Considering to use the human LH/hCG receptors as therapeutic drugs and analytical reagents for humans, it is necessary to make clear the structure and properties thereof.